Abstract: DESCRIPTION (provided by applicant): Our long-range goal is to
understand how the neural mechanisms for pursuit and saccadic eye
movements operate in health and in various human disease states and how
these motor mechanisms are related to higher-level functions. Although
pursuit and saccades have long been viewed as distinct motor systems,
recent work from our lab and others has shown that certain crucial
processing stages are shared. This shared processing likely ensures that
pursuit and saccades are properly coordinated with each other and with
visual perception and cognition during normal behavior.

The objective of
this application is to increase our understanding of this functional
overlap. In particular, we will examine the role of the frontal eye
fields (FEF) in target selection for pursuit and visual judgments about
visual motion, and compare the role of the FEF to that of the superior
colliculus (SC). Our primary hypothesis is that some of the neural
activity in the FEF is related to general estimates of target position
and velocity that are agnostic about the eye motor output; consequently,
these signals would be expected to support visual judgments as well as
target selection for pursuit and saccades.

The project will address the
following three questions: (1) Does the SC contribute to the process of
visual discrimination in addition to its role in target selection? (2)
Does the FEF play a role in target selection for pursuit, and if so, how
does this role compare to its contributions to visual discrimination?
(3) Does the FEF contribute to the visual judgments involving motion?

At
the completion of this research, we expect to understand how activity in
the SC and FEF is related to the mechanisms of target selection for
pursuit, as well as saccades, and to have clarified the relationship
between target and visual selection involving motion. The relevance of
this research to public health. These studies are an important step
toward understanding how the brain coordinates the components of
voluntary movements and how it establishes and regulates the link
between visual processing and motor control. These studies will
therefore help refine clinical descriptions of the oculomotor system
that are used to diagnose eye movement disorders in humans.
Understanding how these systems interact will also help us understand
how and why these circuits malfunction in a variety of developmental
disorders.

Under isoflurane anesthesia and aseptic conditions, we attached a
head-holder using dental acrylic and titanium screws. The head-holder
allowed us to fix the head in the standard stereotaxic position during
experiments. During the same surgery, we also implanted a search coil
around each eye (Judge et al., 1980 ). The coils were used to monitor
eye position with the electromagnetic induction technique (Fuchs and
Robinson, 1966 ). After initial behavioral training, we affixed a
recording chamber for SC single-neuron recording to the skull in a
second surgical procedure. The chamber was angled 38o to the posterior
of vertical and directed at the midline, 15 mm above and 1 mm posterior
to the inter-aural line.

Neurons identified as rostral buildup neurons were then studied with
the gap paradigm illustrated in Figure 2. At the beginning of each
experimental trial, the monkey fixated a small spot stimulus (0.2o
diameter) that appeared at the center of the display. During this
fixation period, which had a randomized duration of 500–1000 msec, the
monkey was required to remain within 2o of the central target;
otherwise, the fixation spot was extinguished and the paradigm reverted
to the fixation period after a 2500 msec timeout. At the end of the
fixation period, the central spot was extinguished and a second small
spot stimulus appeared at a slightly eccentric location along the
horizontal meridian. On pursuit trials, this second stimulus appeared at
2o and moved horizontally toward and through the center of the display
at a constant speed of 15o/sec.

The second stimulus appeared either
immediately after the offset of the fixation spot (no-gap trials) (Fig.
2 A) or after a delay of 200 msec (gap trials) (Fig. 2C). The small
offset in the position of the target stimulus allowed us to elicit
pursuit with few or no accompanying saccades (Rashbass, 1961 ), which
would have otherwise confounded our analysis of pursuit-related
activity. Any pursuit trials containing a saccade in a 600 msec interval
beginning 100 msec before target onset were excluded from analysis.

The
target stimulus always moved horizontally toward the center of the
display, and its starting location was always either inside the response
field of the neuron under study or in the opposite hemifield. On saccade
trials (Fig. 2 B,D), the second stimulus appeared at 3.5o and remained
stationary. Once the second stimulus appeared, the monkey was allowed
500 msec to get its eyes within 3o of the stimulus position and was
required to stay within 3o of the target for the remainder of the trial.
The monkey was given a liquid reward at the end of each trial performed
correctly.

The target on saccade trials was placed at slightly more
eccentric locations than on pursuit trials to avoid the increase in
saccade latencies and the interference with the gap effect, observed
with target eccentricities of 2° (Weber et al., 1992 ; Krauzlis and
Miles, 1996b ). As on pursuit trials, the target stimulus was located
either within the response field of the neuron under study or in the
opposite hemifield.

To protest the inhumane
use of animals in these experiments:
Please email: Richard J. Krauzlis at rich@salk.edu orPhone: (858) 453-4100 ext 1257 Fax: (858) 445-7933. We would also love to know about your efforts with this
cause:
saen@saenonline.org

Rats, mice, birds, amphibians and other animals have
been excluded from coverage by the Animal Welfare Act. Therefore research
facility reports do not include these animals. As a result of this
situation, a blank report, or one with few animals listed, does not mean
that a facility has not performed experiments on non-reportable animals. A
blank form does mean that the facility in question has not used covered
animals (primates, dogs, cats, rabbits, guinea pigs, hamsters, pigs,
sheep, goats, etc.). Rats and mice alone are believed to comprise over 90%
of the animals used in experimentation. Therefore the majority of animals
used at research facilities are not even counted.